Fluid sensor

ABSTRACT

A fluid sensing apparatus and method for detecting pressure and the presence of bubbles within a fluid tube. The fluid sensor comprises a housing configured to receive a portion of the tube and to house the pressure sensor and the ultrasonic transmitter. The pressure sensor is positioned adjacent the tube and is configured to receive a pressure sensor signal, which correlates to a detected pressure differential within the tube. A controller transmits a drive signal to the ultrasonic transmitter, which emits ultrasonic waves through a portion of the tube and to the pressure sensor. The pressure sensor receives both the ultrasonic waves and a pressure sensor signal, and subsequently transmits an output signal to the controller. In the presence of a pressure differential or a bubble within the tube, the output signal will exhibit a DC shift or a distortion of its signal characteristics, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional Application16/409,496, entitled “FLUID SENSOR” and filed on May 10, 2019, which isincorporated herein by reference in its entirety.

BACKGROUND

Fluid sensors are used today to characterize fluids in a wide variety ofapplications including, for example, medical applications. Inparticular, fluid sensors may be incorporated as components of safetymeasures associated with intravenous infusions, a treatment measure inthe daily routine of modern hospitals. Intravenous infusions utilizeinfusion pumps to administer fluids such as nutrients, blood, andmedication intravenously to patients in controlled amounts.

Accordingly, a need exists for improved sensors characterized by a lowerror rate and minimized footprint.

BRIEF SUMMARY

Various embodiments relate to a fluid sensor contained within a singularhousing that is configured to detect pressure changes and to detect thepresence of air bubbles in-line while minimizing both the error rate andthe footprint of the sensor. Various embodiments are directed to a fluidsensor comprising an ultrasonic transmitter configured to emitultrasonic signals through an emitting face, a pressure sensorconfigured to detect pressure changes through a receiving face and toreceive ultrasonic signals from the ultrasonic transmitter, and acontroller, wherein the emitting face of the ultrasonic transmitter maybe spaced apart from the receiving face of the pressure sensor tocollectively define a gap configured to receive a fluid delivery conduittherein, and wherein the controller is configured to detect the presenceof at least one bubble flowing through a fluid delivery conduitpositioned within the gap based at least in part on a frequency-basedanalysis of a pressure sensor output signal. The emitting face of theultrasonic transmitter and the receiving face of the pressure sensor maycollectively define a gap. The gap may be adjustable to compress a fluiddelivery conduit within the gap and between the emitting face of theultrasonic transmitter and the receiving face of the pressure sensor.The pressure sensor may be configured to detect a change in pressurewithin a fluid delivery conduit compressed within the gap and monitorultrasonic signals received from the ultrasonic transmitter to detectbubbles flowing through the fluid delivery conduit compressed within thegap.

In various embodiments, the fluid sensor may comprise an ultrasonictransmitter configured to emit ultrasonic signals through an emittingface and a pressure sensor configured to detect pressure changes througha receiving face, wherein the emitting face of the ultrasonictransmitter is spaced apart from the receiving face of the pressuresensor to collectively define a gap configured to receive a fluiddelivery conduit therein; and wherein the pressure sensor is configuredto detect a change in pressure within a fluid delivery conduitpositioned within the gap; and receive ultrasonic signals from theultrasonic transmitter to detect bubbles flowing through the fluiddelivery conduit positioned within the gap. In various embodiments, thefluid sensor may further comprise a housing, wherein the housingcomprises an exterior housing portion and an interior housing portion,and wherein the ultrasonic transmitter and the pressure sensor areenclosed within the interior housing portion. In various embodiments,the housing may be blow-molded, injection molded, or manufactured by anyother suitable means. In various embodiments, the interior housingportion further defines a channel configured to secure at least aportion of the fluid delivery conduit within the interior portion of thehousing and wherein at least a portion of the channel defines the gap.Further, in various embodiments, a portion of the fluid delivery conduitpositioned within the gap is compressed such that the at leastsubstantially all of the receiving face of the pressure sensor isengaged by a portion of the fluid delivery conduit.

In various embodiments, the pressure sensor may comprise a pressuresensing element mounted to a substrate and a force transmitting memberpositioned adjacent to the pressure sensing element, wherein the forcetransmitting member transmits a force applied to the front side of theforce transmitting member to the front side of the pressure sensingelement. In various embodiments, the force transmitting member may be agel.

In various embodiments, a controller may be configured for wirelesscommunication of an output signal. Further, in various embodiments, theultrasonic transmitter is configured to receive a drive signal from acontroller, wherein the drive signal comprises at least one of an ACcomponent or a DC component. In various embodiments the ultrasonictransmitter may comprise a piezoelectric ultrasonic transducer, and mayfurther comprise an ultrasonic generator. In various embodiments, thefluid sensor may be configured to detect a change in pressure within afluid delivery conduit based at least in part on a detected shift in areceived signal. Further, in various embodiments, the controller may beconfigured to construct transformed data by performing a Fast FourierTransform of the pressure sensor output signal, wherein the transformeddata is indicative of the strength of the pressure sensor output signalacross a frequency range. In various embodiments, the fluid sensor mayconfigured to detect the presence of at least one bubble flowing throughthe fluid delivery conduit by measuring the detected change in thetransformed data at a frequency that is at least substantially similarto a drive frequency of the ultrasonic transmitter. In variousembodiments, the controller may be configured to construct transformeddata by utilizing a bandpass filter centered at a frequency at leastsubstantially similar to a drive frequency of the ultrasonic transmitterto selectively distinguish the pressure sensor output signal at theultrasonic transmitter drive frequency from the noise present within thesignal.

Various embodiments may be directed to a method of detecting occlusionand the presence of bubbles within a fluid delivery conduit, the methodcomprising: detecting a change in pressure within a fluid deliveryconduit based at least in part on a detected shift in a received signaland detecting an air bubble within the fluid delivery conduit based atleast in part on a detected change in transformed data indicative of atleast a portion of the pressure sensor output signal, wherein a signaloutput by the pressure sensor comprises both an AC and a DC component.In various embodiments, the method may further comprise emittingultrasonic signals from an ultrasonic transmitter, through the fluiddelivery conduit, and to a pressure sensor aligned with the ultrasonictransmitter on an opposite side of the fluid delivery conduit andconfigured to receive the ultrasonic signals emitted from the ultrasonictransducer. In various embodiments, the signal emitted from theultrasonic transmitter comprises an AC signal. In various embodiments, aDC shift in the pressure sensor’s output signal corresponds to a changein pressure within the fluid delivery conduit. In various embodiments,the method may further comprise communicating the pressure sensor’soutput signal to one or more external devices. In various embodiments, acontroller is configured for wireless communication of an output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 schematically illustrates communication among various componentsin accordance with some embodiments discussed herein.

FIG. 2 schematically illustrates an exemplary sensor in accordance withvarious embodiments.

FIG. 3 illustrates a cross-sectional view of an exemplary apparatus asdescribed herein without a bubble in the fluid delivery conduit.

FIG. 4 illustrates a cross-sectional view of an exemplary apparatus asdescribed herein with a bubble in the fluid delivery conduit.

FIG. 5 illustrates data flows among components in accordance with someembodiments discussed herein.

FIG. 6 shows an exemplary test configuration in accordance with variousembodiments.

FIG. 7 shows an exemplary graphical representation of signals producedby a testing configuration in accordance with various embodiments.

FIG. 8 shows an exemplary graphical representation of signals producedby a testing configuration in accordance with various embodiments.

DETAILED DESCRIPTION

The present disclosure more fully describes various embodiments withreference to the accompanying drawings. It should be understood thatsome, but not all embodiments are shown and described herein. Indeed,the embodiments may take many different forms, and accordingly thisdisclosure should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will satisfy applicable legal requirements. Like numbersrefer to like elements throughout.

Overview

Described herein is a fluid sensor configured to characterize andmonitor the fluid within a fluid delivery conduit. In an exampleimplementation, a fluid sensor as discussed herein may be utilized tomonitor fluid in tubes utilized in a medical environment (e.g., bloodflow tubes, fluid delivery tubes, and/or the like). The fluid sensordiscussed herein may be configured to utilize non-invasive ultrasonictechnology to detect the presence of air bubbles within a tube. Suchconfigurations are capable of point and continuous sensing, able todetect small bubbles, efficient with respect to power consumption,durable, compatible with a variety of tubing materials, and lesssensitive to particle accumulation. The fluid sensor of certainembodiments described herein exhibits the aforementioned advantages,while further comprising components that enable both low-cost productionand a decreased sensor footprint. Critically, a minimized sensorfootprint may, in certain applications (e.g., medical infusion), enablemonitoring at a point of entry into a patient’s body, which may resultin a more accurate dosage delivery.

As described herein, the fluid sensor may detect pressure changes withinthe tube, which may be caused by, for example, an occlusion causing adecrease or increase in fluid pressure within the tube due to a blockagewithin the tube (which may be detected in light of either an increase ora decrease in pressure within the tube depending on whether the blockageis upstream or downstream from the sensor). The sensor may also detectbubbles, which as described herein encompass a volume of gas having asurface defined as an interface between the gaseous fluid (within theinterior of the bubble) and a liquid fluid (at least partiallysurrounding the exterior of the bubble).

A fluid sensor in accordance with various embodiments may be configuredas described in co-pending U.S. Appl. No. 16/370,099, filed Mar. 29,2019, which is incorporated herein by reference in its entirety. Fluidsensors as discussed herein comprise both a pressure sensor and anultrasonic transmitter, and characterize the flow in a tube positionedbetween the pressure sensor and the ultrasonic transmitter by measuringthe in-line fluid pressure and detecting in-line air bubbles. The fluidsensor further comprises a housing configured receive at least a portionof a fluid delivery conduit, and to house the pressure sensor and theultrasonic transmitter. Within the housing, the pressure sensor ispositioned on one side of the fluid delivery conduit and the ultrasonictransmitter is positioned across from the pressure sensor on an oppositeof the tubing; the two elements are aligned so as to face one anothersuch that the ultrasonic transmitter emits ultrasonic signals throughthe fluid delivery conduit and into the face of the pressure sensor. Toensure the accuracy of the pressure sensor output, the portion of thefluid delivery conduit enclosed within the housing may be compressedsuch that at least a portion of the face of the pressure sensor is incontact with the wall of the fluid delivery conduit. In particularembodiments, at least substantially all of the face of the pressuresensor is in contact with the wall of the fluid delivery conduit.Alternatively, the pressure sensor and the ultrasonic transmitter may bepositioned adjacent to one another on the same side of the fluiddelivery conduit. The two elements may be aligned so as to face into thefluid delivery conduit in substantially the same direction such that theultrasonic transmitter may emit ultrasonic signals through the fluiddelivery conduit and into a reflector element positioned to reflect theemitted signals back through the fluid delivery conduit and into theface of the pressure sensor.

The pressure sensor may comprise a pressure sensing element, which may,for example, be embedded in a coupling gel or some other forcetransmitting member such that low frequency, pressure-related signalsdetected as occurring within the tube (e.g., caused by occlusion) aresensed by the pressure sensing element as the gel transmits the signalfrom the tube (e.g., from the surface of the tube in contact with asurface of the force transmitting member). Such a configuration allowsfor the ultrasonic transmitter to emit high frequency signals throughthe tube and through the gel before reaching the pressure sensingelement, thereby enabling the sensor’s bubble detection functionality.The fluid sensor of certain embodiments detects AC and DC signalcomponents of a signal transmitted from the ultrasonic transmittingmember to characterize the in-line flow: the DC component is utilized todetect changes in pressure within the tube (e.g., which may be caused byocclusion), while the AC component is utilized for the bubble detection.In various embodiments, the fluid sensor may perform a Fast FourierTransform (FFT) to convert the pressure sensor output signal into thefrequency domain. The fluid sensor of certain embodiments determines thestrength of the output signal at the ultrasonic transmitter frequencyand, understanding the characteristics of a signal during both abaseline fluid-in-tube condition and an air-in-tube condition,correlates a more pronounced signal at a frequency of interest (e.g.,the drive frequency) to the presence of an in-line bubble. As designed,the fluid sensor effectively reduces error rate by utilizing a dualsensor configuration (i.e. the simultaneous AC and DC signal components)to be used to compensate for inaccurate variations in the sensor’sreading resulting from drifts in the acoustic baseline due tounwarranted changes in contact force (e.g., tubing deformation,temperature change, fluid pressure, etc.).

Housing/Sensor Construction

As shown in FIGS. 1-3 , the fluid sensor 10 comprises a housing 100. Thehousing 100 defines the exterior of the fluid sensor 10 and may have aheight, length, and a width, wherein the length of the housing 100 isdefined by the distance between a first end and a second end. Asillustrated in FIG. 1 , the housing may further comprise a channel 113extending from the first end of the housing 100 to the second end andconfigured to receive and secure at least a portion of a fluid deliveryconduit. Housing 100 may be configured to enclose both the pressuresensor 200 and the ultrasonic transmitter 300 within the interiorportion of the housing. The pressure sensor 200 and the ultrasonictransmitter 300 are each coupled to an interior portion of the housing110 and are spaced apart within the interior portion of the housing 110to define a gap 114 between the two elements. In various embodiments,the width of the gap 114 may be substantially equal to the width of thechannel 113 and may run parallel to (and/or coextensive with) at least aportion of the channel 113. The pressure sensor 200 and the ultrasonictransmitter 300 of the illustrated embodiment are aligned within thehousing 100 so as to face one another; that is, the emitting face of theultrasonic transmitter 301 should be facing toward the receiving face ofthe pressure sensor 201 such that high frequency waves generated by theultrasonic transmitter 300 and emitted from the emitting face of theultrasonic transmitter 301 travel towards the receiving face of thepressure sensor 201. In such an exemplary configuration, the pressuresensor 200 and the ultrasonic transmitter 300 may be arranged to face adirection perpendicular to the length of the channel 113, and may defineat least a portion of the channel 113.

In various embodiments, the fluid delivery conduit may have a length,and a diameter, and may comprise an outer circumferential wall, an innercircumferential wall, and a wall thickness extending between the outercircumferential wall and the inner circumferential wall; and an interiorchannel within the inner wall configured to direct the flow of fluidfrom one location to a second location. The fluid delivery conduit maycomprise a resilient material (e.g., a silicone material, a polyvinylchloride material, and/or the like).

The housing 100 may be configured to receive at least a portion of afluid delivery conduit 120 through the channel. A portion of fluiddelivery conduit 120 may extend from a first end of the housing 111 to asecond end of the housing 112. The fluid delivery conduit 120 may bepositioned within the channel 113 such that it runs parallel to andintersects the gap 114. In such a configuration, at least a portion ofthe fluid delivery conduit 120 is between the pressure sensor 200 andthe ultrasonic transmitter 300. In such an exemplary configuration, thepressure sensor 200 and the ultrasonic transmitter 300 may be arrangedto face a direction perpendicular to the length of the fluid deliveryconduit 120. Further, the pressure sensor 200 and the ultrasonictransmitter 300 may be centered at the same position along the length ofthe fluid delivery conduit such that the gap 114 between the twoelements is substantially perpendicular to the length of the fluiddelivery conduit.

As described above and as illustrated in FIGS. 2-4 , at least a portionof the fluid delivery conduit 120 may be positioned between and adjacentto the pressure sensor 200 and the ultrasonic transmitter 300 such thatwhen the ultrasonic transmitter 300 emits signals (e.g., high frequencyultrasonic signals) in the direction of the pressure sensor 200, thesignals pass through a cross-section of the fluid delivery conduit 120.The housing 100 may be adjustably configured such that the width of thegap 114 between the pressure sensor 200 and the ultrasonic transmitter300 may be smaller than the diameter of fluid delivery conduit 120,thereby causing a compression force to be applied to a portion of theouter wall of the fluid delivery conduit 120 secured within the gap 114.The compression force may be applied in a direction perpendicular to thelength of the fluid delivery conduit 120 such that the outer wall of thefluid delivery conduit 120 is pressed against the receiving face of thepressure sensor 201. In such an exemplary configuration, the appliedcompression force may be sufficient to cause at least substantially allof the receiving face of the pressure sensor 201 to be engaged by thecompressed outer wall of the fluid delivery conduit 120. In variousembodiments, the compression force may be user-defined and/or dependenton one or more characteristics of the fluid delivery conduit 120 suchas, for example, wall thickness, material type, outer diameter, innerdiameter, and any other characteristic of the fluid delivery conduit120. In various embodiments, the fluid sensor 10 may be furtherconfigured to monitor a compressive force applied to a portion of thefluid delivery conduit 120 positioned between the receiving face of thepressure sensor 201 and the ultrasonic transmitter 300 (e.g., using anancillary pressure sensor). The measured compressive force applied tothe portion of the fluid delivery conduit 120 may be utilized in certainembodiments to calibrate pressure sensor 200 readings of pressure withinthe fluid delivery conduit 120. In other embodiments, the fluid sensor10 may be separately calibrated for pressure sensor 200 readings ofpressure within the fluid delivery conduit 120.

In some embodiments, the fluid sensor 10 may be connected to a powersupply 130 configured to receive power and power the fluid sensor. Asnon-limiting examples, the power supply 130 may comprise one or morebatteries, one or more capacitors, one or more constant power supplies(e.g., a wall-outlet), and/or the like. In some embodiments, as shown inFIG. 2 , the power supply 130 may comprise an external power supplypositioned outside of the housing 100 and configured to deliveralternating or direct current power to the fluid sensor 10. Further, insome embodiments, as illustrated in FIG. 3 , the power supply 130 maycomprise an internal power supply, for example, one or more batteries,positioned within the housing 100.

In various embodiments, power may be supplied to controller 140 toenable distribution of power to the various components described herein.In some embodiments, each of the components of the fluid sensor 10 maybe connected to controller 140 (e.g., for electronic communication),which may be configured to facilitate communication and functionalcontrol therebetween. In various embodiments, the controller 140 maycomprise one or more of a processor, memory, a communication module, anon-board display 150, and signal analysis circuitry. For example, thecontroller 140 may comprise a driving circuit and a signal processingcircuit. In various embodiments, the controller 140 may be configured topower the pressure sensor 200 and/or receive an output signal from thepressure sensor 200. In various embodiments, the controller 140 may beconfigured to power the ultrasonic transmitter 300 and/or transmit adrive signal to the ultrasonic transmitter 300. In various embodiments,as shown in FIGS. 3 and 4 , the controller may be configured to transmitoutput signals out to external components via universal serial bus (USB)or any other wired connection. In various embodiments, an on-boarddisplay may be configured to display a variety of signals transmittedfrom or received by the controller 140, and/or the like. In variousembodiments, the controller may be embodied as a single chip (e.g., asingle integrated-circuit chip) configured to provide power signals toboth the pressure sensor 200 and the ultrasonic transmitter 300, toreceive and process the output signal from the pressure sensor 200,and/or to compensate for any detected changes in environmental factorssuch as, for example, temperature, flow, or pressure within the fluiddelivery conduit 120. Such a configuration may be desirable to minimizeproduction costs and reduce the physical footprint of the fluid sensor10.

As described above and as will be appreciated based on this disclosure,various embodiments may be configured in various forms including withportions of the fluid sensor 10 shown in FIG. 5 being remote from theapparatus. In various embodiments, all of the components necessary tocharacterize the flow through a fluid delivery conduit 120 may beintegrated into a single housing 100. In various embodiments, thecontroller 140 may be configured to communicate with a variety ofexternal devices via Bluetooth™, Bluetooth Low Energy (BTLE), Wi-Fi™, orany other wireless connection. As shown in FIG. 5 , the controller maybe configured so as to enable wireless communication within anInternet-of-Things (IoT) network 500 to a variety of wirelessly enableddevices (e.g., a user mobile device 501, a server 502, a computer 503,and/or the like).

In various embodiments, the controller 140 may comprise signal analysiscircuitry, which may be configured to perform frequency based analysisof a pressure sensor output signal to determine whether a bubble ispresent within the fluid delivery conduit 120. For example, the signalanalysis circuitry may receive the pressure sensor output signal andperform a Fast Fourier Transform (FFT) to observe a signalrepresentation in the frequency domain. In various embodiments, thesignal analysis circuitry may be configured to analyze the transformeddata and further to detect a bubble in the fluid delivery conduit 120based at least in part on, for example, one or more of the measuredstrength of the signal at the known ultrasonic transmitter drivefrequency, a signal contrast ratio between a measured signal and abaseline fluid-in-tube condition to an in-line bubble, and asignal-to-noise ratio of the transformed data at the ultrasonictransmitter drive frequency. In various embodiments, the transformeddata may indicate a distinguishably higher signal strength at theultrasonic transmitter drive frequency during an air-in-tube conditioncompared to the signal strength at the ultrasonic transmitter drivefrequency during a fluid-in-tube condition. In various embodiments, themeasured signal strength value may vary based on, for example, one ormore of fluid delivery conduit 120 size, fluid delivery conduit 120material, ultrasonic signal strength, signal amplifier gain, and anyother applicable parameter specific to the implemented embodiment. Invarious embodiments, an air-in-tube condition may be detected bycomparing the signal-to-noise ratio of the transformed data in anair-in-tube condition to that of the transformed data in a fluid-in-tubecondition at the ultrasonic transmitter drive frequency. For example, ahigh signal contrast ratio may be indicative of the presence of a bubblewithin the tube. In various embodiments, a signal contrast ratio ofbetween 2 and 5 (e.g., 3) may be measured when comparing theaforementioned respective transformed data. As described herein, whenthe fluid sensor 10 detects a signal contrast ratio as described aboveat the ultrasonic transmitter drive frequency with a value of at least 1kHz, the controller 140 may be configured to determine that a bubble ispresent in the fluid delivery conduit 120.

In various embodiments, the signal analysis circuitry may furthercomprise a bandpass filter configured to isolate one or more signals ofinterest within a particular band of frequencies. In variousembodiments, the bandpass filter range may be centered at the drivefrequency of the ultrasonic transmitter and may be configured to allow arange of frequencies between, for example, within 500 Hz above and/orbelow the drive frequency to be received (e.g., a 1 kHz band). Invarious embodiments, the bandpass filter may be used to selectivelydistinguish the signal at the ultrasonic transmitter drive frequencyfrom the noise present within the signal. In certain embodiments, thebandpass filter may sufficiently isolate the drive frequency of theultrasonic transmitter that characteristics of the output signal (e.g.,in the time-domain) may be utilized to detect the presence of a bubblewithin the fluid delivery conduit. For example, signal amplitude,detected presence (or absence) of a signal at the drive frequency,and/or the like may be utilized to determine whether a bubble is presentwithin the fluid delivery conduit. It should be understood that thebandpass filter may be embodied as hardware and/or software. In variousembodiments, the signal analysis circuitry may further comprise a signalamplifier configured to increase the strength of the pressure sensoroutput signal. In various embodiments, the signal amplifier may be usedto strengthen the pressure sensor output signal so as to ensure that thesignal at the ultrasonic transmitter drive frequency may be detected bythe signal analysis circuitry.

The use of the term “circuitry” as used herein with respect tocomponents of the fluid sensor 10 therefore includes particular hardwareconfigured to perform the functions associated with respective circuitrydescribed herein. Of course, while the term “circuitry” should beunderstood broadly to include hardware, in some embodiments, circuitrymay also include software for configuring the hardware. For example, insome embodiments, “circuitry” may include processing circuitry, storagemedia, network interfaces, input-output devices, and other components.In some embodiments, other elements of the controller 140 may provide orsupplement the functionality of particular circuitry. For example, theprocessor may provide processing functionality, memory may providestorage functionality, and communication module may provide networkinterface functionality, among other features.

Pressure Sensor

As shown in FIGS. 1-4 , the fluid sensor 10 may comprise a pressuresensor 200. The pressure sensor may be embodied as a pressure sensorsuch as that described in U.S. Patent Publ. No. 2018/0306659, which isincorporated herein by reference in its entirety. In variousembodiments, the pressure sensor 200 may comprise a printed circuitboard 210, a pressure sensing element 220, a sidewall 240, and a forcetransmitting member 250. As described above, the pressure sensor may bepositioned within the housing 100 and coupled to an interior portion ofthe housing 100. The pressure sensor 200 may further comprise areceiving face 201, which may be, for example, either a flat, convex, orconcave surface. The pressure sensor may be arranged such that thereceiving face 201 is aligned with and facing the emitting face of theultrasonic transmitter 301. The receiving face of the pressure sensor201 may be spaced apart from the emitting face of the ultrasonictransmitter 301 at a distance defining the gap 114.

The substrate 210 of the pressure sensor 200 may be any type of printedcontrol board (PCB), a ceramic substrate, or other suitable substrateconfiguration. In some embodiments, the substrate 210 may be a thickfilm printed ceramic board, however other circuit board configurationsmay be utilized in other embodiments. In one example, the substrate 210may be made, at least in part, of FR 4 laminate and/or other material.In various embodiments, the substrate 210 may have one or moreelectronic components thereon and/or pads for connecting to electroniccomponents of a device in which the pressure sensor 200 may be insertedor with which the pressure sensor 200 may be used. In one example, thesubstrate 210 may include an application specific integrated circuit(ASIC) that may be attached to the substrate 210. Such an ASIC may beelectrically connected to the substrate 210 via wire bonds, bump bonds,electrical terminals, and/or any other suitable electrical connections.Additionally or alternatively, the substrate 210 may include one or moreconductive pads for engaging circuitry and/or electronic components incommunication with a remote processor or the like.

Further, the substrate 210 may include one or more processingelectronics and/or compensation circuitry (e.g., which may or may notinclude an ASIC). Such processing electronics may be electricallyconnected to terminals of the pressure sensing element 220, an ASIC (ifpresent), and/or electrical terminals to process electrical signals fromthe pressure sensing element 220 and/or to transfer outputs from thepressure sensing element 220 to electronic components of one or moredevices used in conjunction with the pressure sensor 200. In someinstances, the substrate 210 may include circuitry that may beconfigured to format one or more output signals provided by the pressuresensing element 220 into a particular output format. For example,circuitry of the substrate 210 (e.g., circuitry on one or more of sidesof the substrate 210) may be configured to format the output signalprovided by pressure sensing element 220 into a ratio-metric outputformat, a current format, a digital output format and/or any othersuitable format. In some cases, the circuitry of the substrate 210 maybe configured to regulate an output voltage. Circuitry on the substrate210 for providing a ratio-metric (or other) output may include tracesand/or other circuitry that may serve as a conduit to test pads, and/orfor providing the ratio-metric (or other) output to one or moreelectrical terminals facilitating electrical connections with electroniccomponents of one or more devices used with the pressure sensor 200.

The pressure sensing element 220 of the pressure sensor 200 may beconfigured in any manner and may have a first side 221 (e.g., a frontside) and a second side 222 (e.g., a back side). In some cases, thepressure sensing element 220 may include a micromachined pressure sensedie that includes a sense diaphragm. In various embodiments, thepressure sensing element 220 may be back-side mounted on the substrate210 with the second side of the pressure sensing element 222 facing thesubstrate 210 and may be configured to perform top-side sensing (e.g.sensing with the first side of the pressure sensing element 221). In apressure sensing element 220 configuration, the top-side sensing may bewhen a sensed media either directly or indirectly (e.g., through theforce transmitting member 250 or other intermediary) interacts with atop side of the pressure sensing element 221. Back-side mounting thepressure sensing element 220 to the substrate 210 may facilitatecreating a robust pressure sensor 200 because any sensed media acting onthe pressure sensing element 220 may act to push the pressure sensingelement 220 against the substrate 210. Although the pressure sensingelement 220 may be described herein as being back-side mounted to thesubstrate 210, it is contemplated that the pressure sensing element 220may be mounted relative to the substrate 210 in one or more otherconfigurations. For example, the pressure sensing element 220 may befront side mounted or mounted in any other suitable manner. Further, thepressure sensing element 220 may be electrically connected to thesubstrate 210 in one or more manners. In various embodiments, wire bonds230 may be utilized to electrically connect the pressure sensing element220 to the substrate 210. The wire bonds 230 may have a first endconnected to a bond pad of the pressure sensing element 220 and anotherend connected to a bond pad of the substrate 210. Additionally oralternatively, the pressure sensing element 220 may be electricallyconnected to the substrate 210 via bump bonds and/or in any othersuitable manner.

The sidewall 240 of the pressure sensor 200 may extend from a first end241 to a second end 242. In various embodiments, the sidewall 240 mayentirely or at least partially circumferentially surround and/or enclosethe pressure sensing element 220, wire bonds 230, bond pads, the forcetransmitting member 250, and/or other components of the pressure sensor200. The sidewall 240 may have a cross-section substantially circular orany other suitable shape. The sidewall 240 may be connected to thesubstrate 210 such that the second end of the sidewall 242 may face thesubstrate 210 and the first end of sidewall 240 may be spaced away fromthe substrate 210. In some cases, the sidewall 240 may be attached to atleast a portion of the substrate 210 to provide additional structuralintegrity to the pressure sensor 200. The first end of the sidewall 241may be positioned substantially adjacent the receiving face of thepressure sensor 201 and may at least partially define an opening fromthe first end of the sidewall 241 to the pressure sensing element 220(e.g., a reservoir defined by the sidewall 240). The sidewall 240 may bemade from any type of material. In one example, the sidewall 240 may bemade from a plastic, a metal, a ceramic and/or any other suitablematerial.

In various embodiments, the force transmitting member 250 of thepressure sensor 200 may comprise a first end and a second end, whereinthe first end may be configured to entirely engage a portion of theouter wall of the fluid delivery conduit 120 positioned within the gap114 and the second end may be configured to interact with the pressuresensing element 220. The force transmitting member 250 may fill or atleast partially fill the opening and/or reservoir of the sidewall 240.In various embodiments, the force transmitting member 250 may beconfigured to facilitate transferring a force interacting with the firstend of the force transmitting member 250 to the pressure sensing element220. In such an exemplary configuration, the force experienced by thepressure sensing element 220 may arise due to a change in pressurewithin the fluid delivery conduit 120 caused by a pressure change event(e.g., occlusion) and may result in a shift in the DC signal produced bythe pressure sensor 200.

The force transmitting member 250 may be formed from one or more layersof material. For example, the force transmitting member 250 may beformed from one layer of material, two layers of material, three layersof material, four layers of material, five layers of material, or othernumber of layers of material. The force transmitting member 250 may bemade from any suitable material. In various embodiments, the forcetransmitting member 250 may comprise a dielectric material, anon-compressible material, a biocompatible material, colored material,non-colored material, and/or one or more other types of material.Further, in various embodiments the force transmitting member 250 maycomprise a gel (e.g., a fluoro-silicone gel), a resilient material suchas a cured silicone rubber or silicone elastomer, a cured liquidsilicone rubber, an oil and/or any other suitable material. In variousembodiments, the force transmitting member 250 may include abiocompatible material such as, for example, a cured silicone elastomer,that is medically safe to directly contact medicines or the like thatare to be provided to a patient. In various embodiments wherein theforce transmitting member 250 comprises a gel, the pressure sensor mayfurther comprise a membrane configured to cover the entirety of theopening at the first end of the sidewall 240 so as to contain the gelwithin the cavity.

In various embodiments, the pressure sensor 200 may be electronicallyconnected to the controller 140 such that the controller 140 transmits apower signal to the pressure sensor 200. In various embodiments, thepressure sensor 200 may be powered at a voltage of between 1.5 volts and15 volts (e.g., 5 volts). The pressure sensor 200 may be configured to,upon sensing both a pressure sensor signal created by a pressuredifferential within the fluid delivery conduit 120 and a high frequencyultrasonic waves from the ultrasonic transmitter 300, transmit an outputsignal comprising both an AC component and a DC component to thecontroller 140.

Ultrasonic Transmitter

As shown in FIGS. 1-4 , the fluid sensor 10 may comprise an ultrasonictransmitter 300, which, in various embodiments, may be coupled to theinterior portion of the housing 110. The ultrasonic transmitter 300 maydefine an emitting face 301 and may be arranged such that the emittingface 301 is aligned with and facing the receiving face of the pressuresensor 201. The emitting face of the ultrasonic transmitter 301 may bespaced apart from the receiving face of the pressure sensor 201 at adistance defining the gap 114. As illustrated in FIGS. 3 and 4 , theultrasonic transmitter 300 may be configured to generate and emit anultrasonic signal in a direction substantially perpendicular to theemitting face 301, through the fluid delivery conduit 120, and towardsthe receiving face of the pressure sensor 201 such that the signal maybe detected by the pressure sensing element 220.

As is generally understood in the art, the ultrasonic transmitter 300may, in various embodiments, comprise an ultrasonic generator and anultrasonic transducer. In various embodiments, the ultrasonic transducermay be, for example, a piezoelectric ultrasonic transducer. Apiezoelectric ultrasonic transducer may comprise, for example, a ceramicdisc (e.g., PIC255) and wrap-around electrodes configured to establishan electrical connection at a favorable position within the transducerassembly. In various embodiments, the ultrasonic transducer may have adiameter of between 2 mm and 15 mm (e.g., between 5 mm and 10 mm) andmay have a thickness of between 0.5 mm and 4 mm (e.g., between 1 mm and2 mm). In various embodiments, the ultrasonic transmitter 300 may betuned for optimal interaction with and response by the pressure sensingelement 220.

In various embodiments, the ultrasonic transmitter 300 may beelectronically connected to the controller 140 such that the ultrasonictransmitter 300 may be powered by the controller 140. The controller 140may be configured to further supply the ultrasonic transmitter 300 witha fixed frequency drive signal generally in the form of an oscillatingsignal, such as a sine-wave, square wave, triangular wave, sawtoothwave, and/or the like. However, it should be understood that othersignal shapes may be provided as discussed herein. In variousembodiments, the drive signal sent from the controller 140 to theultrasonic transmitter 300 may manifest as a voltage centered between1.5 volts and 100 volts (e.g., 5 volts). The ultrasonic transmitter 300may be configured to receive the signal from the controller 140 and emithigh frequency ultrasonic waves through the emitting face 301 and acrossa portion of the fluid delivery conduit 120 such that it may be receivedby the pressure sensor 200.

Pressure Sensing

As described herein, the fluid sensor 10 may be configured to detectocclusion (or other fluid pressure-changing events) within a fluiddelivery conduit 120 by detecting a change in pressure within the fluiddelivery conduit 120. As shown in FIGS. 2-4 , the pressure sensor 200 ofthe fluid sensor 10 may be located within the interior of the housing110 and arranged such that the receiving face of the pressure sensor 201is at least substantially parallel and adjacent to a length of thechannel 113 configured to receive and secure at least a portion of thefluid delivery conduit 120. Similarly, the emitting face of theultrasonic transmitter 301 may be positioned at least substantiallyparallel to both the receiving face of the pressure sensor 201 and thelength of the channel 113 configured to receive and secure at least aportion of the fluid delivery conduit 120. In such an exemplaryconfiguration, the pressure sensor 200 (e.g., the receiving face of thepressure sensor 200) engages a portion of the outer wall of the fluiddelivery conduit 120 located within the interior portion of the housing110 such that pressure within the fluid delivery conduit 120 may exert aforce onto the receiving face of the pressure sensor 201. The forceexerted on the pressure sensor 200 may be detected by the forcetransmitting member 250, which may be configured to transmit at least aportion (e.g., all) of the force to the pressure sensing element 220. Invarious embodiments, the force transmitting member 250 may comprise, forexample, a gel.

As described above, the pressure sensing element 220 may be configuredto receive high frequency signals (e.g., oscillating signals) emitted bythe ultrasonic transmitter 300. The signal emitted by the ultrasonictransmitter 300 is received by the pressure sensing element 220 aftertraveling through the fluid delivery conduit 120.

In various embodiments, an occlusion within the fluid delivery conduitmay result in a change of pressure within the fluid delivery conduit120, and thus, a change in force being exerted on the inner wall of thefluid delivery conduit 120 and, in turn, a change in force beingtransmitted from the fluid delivery conduit 120 to the pressure sensor200. The change in force arising from a change in pressure within thefluid delivery conduit 120 may define a low frequency event received byand transmitted through the force transmitting member 250 such that itmay be sensed by the pressure sensing element 220. In variousembodiments, a low frequency event experienced by the pressure sensingelement 220 may be detected as a shift in signal detected by thepressure sensing element 220 (e.g., correlating to a DC shift). Such achange in the signal to the pressure sensing element 220 may manifest ina proportional DC shift experienced by the pressure sensor’s outputsignal to the controller 140. For example, when the fluid within thefluid delivery conduit 120 experiences occlusion, the resultant changein pressure leads to a change signal voltage output by the pressuresensing element, and thus, a vertical shift of the output signal.Accordingly, in various embodiments, the fluid sensor 10 may beconfigured to detect occlusion within a fluid delivery conduit 120 byreceiving the emitted high frequency signal components from theultrasonic transmitter 300 and correlating a detected variance involtage (i.e. DC shifts) in the pressure sensor’s resultant outputsignal to a blockage within the fluid delivery conduit 120.

In various embodiments, to ensure accuracy of the signal detected by thepressure sensing element 220, both the receiving face of the pressuresensor 201 and the emitting face of the ultrasonic transmitter 301 maybe positioned at least substantially parallel to and in contact with aportion of the outer wall of the fluid delivery conduit 120 securedwithin the channel 113. As described above and as shown in FIGS. 3 and 4, the fluid delivery conduit 120 may be compressed in the direction ofthe conduit’s width such that at least substantially all of receivingface of the pressure sensor 201 is in contact with a portion of theouter wall of the fluid delivery conduit 120. Such a configurationenables the entirety of the face of the force transmitting member 250 tobe coupled to the surface of the fluid flowing through the fluiddelivery conduit 120 for the purposes of sensing force, and prevents anyundesirable force “leakage” that is transmitted away from the pressuresensing element 220. In various embodiments, failure to essentiallycouple the pressure sensing element 220 to the fluid being sensedthrough the force transmitting member 250, may result in the forcetransmitting member 250 receiving a distorted signal. Such a distortionmay result in the fluid sensor 10 producing inaccurate readings.

Bubble Detection

As described herein, the fluid sensor 10 may be configured to detect thepresence of an air bubble 302 within a fluid delivery conduit 120 bydetecting a change in the signal (e.g., the oscillating signalcomponent) emitted from the ultrasonic transmitter and received by thepressure sensor 200. For example, the fluid sensor may be configured todetect the presence of an air bubble 302 within a fluid delivery conduit120 by detecting a change in signal strength at a defined frequencyreceived by the pressure sensor 200. As described above and as shown inFIGS. 3 and 4 , the pressure sensor 200 of the fluid sensor 10 may belocated within the interior of the housing 110 and arranged such thatthe receiving face of the pressure sensor 201 is at least substantiallyparallel to a length of the channel 113 configured to receive and secureat least a portion of the fluid delivery conduit 120. Similarly, theemitting face of the ultrasonic transmitter 301 may be positioned atleast substantially parallel to both the receiving face of the pressuresensor 201 and the length of the channel 113 such that the emitting faceof the ultrasonic transmitter 301 and the receiving face of the pressuresensor 201 are spaced apart to define a gap 114 configured to accept thefluid delivery conduit 120 therein.

In such an exemplary configuration, the ultrasonic transmitter 300 maybe configured to receive a drive signal (e.g., an oscillating drivesignal, such as an AC drive signal) from the controller 140 and to emitultrasonic waves carrying the signal through the emitting face of theultrasonic transmitter 301, through the portion of the fluid deliveryconduit 120 positioned within the gap 114, and to the receiving face ofthe pressure sensor 201. In various embodiments, wherein the forcetransmitting member 250 may be, for example, a gel, the gel may act asan incompressible fluid. The emitted signal may be sensed by thepressure sensing element 220, which may be configured to subsequentlytransmit an output signal to the controller 140 indicative of thedetected signal. As described above, the emitted signal may be embodiedas an AC signal or another oscillating signal shape, centered on avoltage characterized by a DC shift in the drive signal.

In an exemplary condition wherein there are no air bubbles presentwithin the fluid delivery conduit 120, as illustrated in FIG. 3 ,substantially all of the waves emitted from the ultrasonic transmitter300 are sensed by the pressure sensor 200, resulting in a signaltransmitted to the controller 140 that is indicative of an uninterruptedsignal transmitted through the fluid delivery conduit 120. Conversely,in an exemplary condition wherein at least one air bubble 302 is presentwithin the fluid delivery conduit 120, as illustrated in FIG. 4 , theair bubble 302 may interrupt the direct transmission of the emittedsignal from the ultrasonic transmitter 300 to the pressure sensor 200and may reflect and/or deflect at least a portion of the emitted signal,deflecting the portion of the signal away from the pressure sensingelement 220. In such an exemplary circumstance, the reflection of atleast a portion of the emitted signal may result in a distorted signalreceived by the pressure sensing element 220 when represented in thetime domain. When the air bubble 302 is present in the fluid deliveryconduit 120, the received signal, when presented in a frequency domain,may exhibit, for example, a pronounced signal at the drive frequency ofthe ultrasonic transmitter 300. Accordingly, in various embodiments, thefluid sensor 10 may be configured to detect the presence of an airbubble 302 within a fluid delivery conduit 120 by monitoring the emittedhigh frequency signal from the ultrasonic transmitter 300 andcorrelating a more pronounced signal at the ultrasonic transmitter 300drive frequency to the presence of a bubble 302 within the fluiddelivery conduit 120. Further, in various embodiments, the fluid sensor10 may be further configured to determine specific characteristics aboutthe detected bubble 302 such as, for example, its size, based on one ormore of the distortions in the signal received by the pressure sensingelement

Signal Analysis

As illustrated in FIGS. 7 and 8 , in various embodiments a Fast FourierTransform (FFT) may convert the pressure sensor 200 output signal totransformed data represented in the frequency domain. In variousembodiments, the FFT may be performed by either the controller 140 or anexternal computer in communication with the sensor 10 and configured toperform the FFT. In various embodiments, the transformed data may beindicative of the strength of the pressure sensor output signal across afrequency range. The transformed data in an air-in-tube condition 490may be discernably different from the transformed data in an air-in-tubecondition 470 at one or more frequencies, such as, for example, theultrasonic transmitter 300 drive frequency. The transformed data in anair-in-tube condition, distinct from that in a fluid-in-tube condition,may comprise a distinguished signal at the frequency along the x-axiscorrelating to the ultrasonic transmitter 300 drive frequency. Invarious embodiments, an air-in-tube condition may be detected bycomparing the signal-to-noise ratio of the transformed data in anair-in-tube condition to that of the transformed data in a fluid-in-tubecondition at the ultrasonic transmitter drive frequency. In variousembodiments, a signal contrast ratio of between 2 and 5 (e.g., 3) may bemeasured when comparing the aforementioned respective transformed data.As described herein, when the fluid sensor 10 detects a signal contrastratio as described above at the ultrasonic transmitter drive frequencywith a value of at least 1 kHz, the controller 140 may be configured todetermine that a bubble is present in the fluid delivery conduit 120.Further, in various embodiments, when the fluid sensor 10 detects asignal-to-noise ratio at the ultrasonic transmitter drive frequency ofat least between 2 and 5 (e.g., 3 ), the controller 140 may beconfigured to determine that a bubble is present in the fluid deliveryconduit 120.

In an alternative embodiment, a bandpass filter configured to facilitatebubble detection by isolating one or more signals of interest within aparticular band of frequencies. The bandpass filter may be implementedto selectively distinguish the signal at the ultrasonic transmitterdrive frequency from the noise present within the signal, therebyproducing transformed data to be analyzed without performing a FFT. Invarious embodiments, the bandpass filter range may be centered at thedrive frequency of the ultrasonic transmitter and may be configured toallow a range of frequencies between, for example, within 500 Hz aboveand/or below the drive frequency to be received (i.e. a 1 kHz band). Invarious embodiments, when the fluid sensor 10 detects a signal at theultrasonic transmitter drive frequency, the controller 140 may beconfigured to determine that a bubble is present in the fluid deliveryconduit 120.

Experimental Testing

Experimental testing was conducted to verify the effectiveness ofembodiments as described herein. Data was collected over the course ofmultiple trials using various combinations of embodiments describedabove.

In the testing configuration, an exemplary fluid sensor used for testingwas configured to be in electronic communication with both the pressuresensor controller and the ultrasonic transmitter controller. Thepressure sensor controller was configured to transmit a power signal tothe pressure sensor. Similarly, the ultrasonic transmitter controllerwas configured to transmit a power signal to the ultrasonic transmitter.The testing circuitry comprised a drive circuit configured to transmit asignal to the ultrasonic transmitter. The testing circuitry was furtherelectronically connected to an oscilloscope configured to generate thedrive signal and graphically display the output signal sensed by thepressure sensor. Example output signals 460, 480 are shown in FIGS. 7and 8 .

FIG. 6 shows a close-up view of the fluid sensor 10 sensory componentsused in the exemplary testing configuration. The pressure sensor 200 issecured to the bottom surface of a vise, a configuration meant torecreate the mounting of the pressure sensor 200 within the interiorportion of the housing 110. Similarly, the ultrasonic transmitter 300 issecured relative to the top surface of the vise. In such aconfiguration, the pressure sensor 200 and the ultrasonic transmitter300 are spaced apart so as to define a gap 114 configured to receive aportion of the fluid delivery conduit 120. As shown in FIG. 6 , thetesting configuration comprised the pressure sensor 200 and theultrasonic transmitter 300 mounted to a vise so as to replicate therequisite compression applied to the fluid delivery conduit 120 whensecured within the housing 100 of the fluid sensor 10. As describedabove, the fluid delivery conduit 120 was compressed by the vise suchthat the entirety of the receiving face of the pressure sensor 201 wascovered by at least a portion of the outer wall of the fluid deliveryconduit 120. The exemplary testing configuration utilized a fluid 303flowing through the tube with deliberately injected air bubbles 302present within the fluid delivery conduit 120 to enable analysis of thesignal sensed by the pressure sensor 200 under conditions both with andwithout air bubbles 302 present within the fluid delivery conduit 120.

FIG. 7 shows a graphical representation of an example pressure sensoroutput signal 460 represented in the time domain and example transformeddata 470, both under baseline fluid conditions. As described above, thecharacteristics of the corresponding ultrasonic transmitter drive signalmay be selected to produce a drive signal shape for use in conjunctionwith the specific testing circuitry. Here, the shape of the exampleultrasonic transmitter drive signal is similar to that of a generalsinusoidal AC signal. As illustrated in FIGS. 7 and 8 , the ultrasonictransmitter drive signal has a frequency selected to be above the normalhearing range of humans. For example, the drive frequency may be 20 kHz,although it should be understood that other frequencies may be utilized.The shape of the example pressure sensor output signal 460, 480—shown inFIGS. 7and 8 —may vary from that shown therein, and generally correlatesto a baseline fluid pressure within a fluid delivery conduit void of airbubbles. The example pressure sensor output signal 460 is centeredaround an axis which may represent a signal shift of, for example, 300mV. Upon detection of a change in pressure, the pressure sensor outputsignal 460 may shift vertically to represent the change in pressure. ADC shift of the pressure sensor output signal 460 may correspond to achange in pressure within the fluid delivery conduit 120 due to, forexample, occlusion.

FIG. 7 further illustrates the resultant transformed data 470 after aFFT has been performed on the pressure sensor output signal 460. Likethe pressure sensor output signal 460, the transformed data 470 isrepresentative of a fluid-in-tube condition. As shown, an 98 µV signal,highlighted by exemplary axis A for reference, was measured at the 20kHz ultrasonic transmitter drive frequency.

FIG. 8 shows an exemplary distorted pressure sensor output signal wavesensed by the pressure sensor 480 and example transformed data, bothdistorted by the presence of a gas bubble within a fluid deliveryconduit 120. As described above, in a condition in which gas bubbles 302are present within the fluid delivery conduit 120, the output signal 480may exhibit characteristics different from those of the output signalunder normal baseline fluid conditions 460. However, depending on, forexample, the input signal characteristics, such differences may be hardto detect in various embodiments. Accordingly, as illustrated by theresultant air-in-tube transformed data 490 in FIG. 8 , a FFT wasperformed on the pressure sensor output signal 480 to represent thesignal in the frequency domain. As shown in FIG. 8 , a 308 µV signal,highlighted by exemplary axis B for reference, was measured at the 20kHz ultrasonic transmitter drive frequency. Notably, the signal measuredat the 20 kHz ultrasonic transmitter drive frequency during anair-in-tube condition was significantly greater than the correspondingsignal measured at the same frequency during a fluid-in-tube condition.In the exemplary test configuration described herein, the signalcontrast ratio between the signal air-in-tube transformed data 490 (308µV) and the signal fluid-in-tube transformed data 470 (98 µV) at 20 kHzwas approximately 3:1. In various embodiments, such transformed datacomprising such an exemplary strong signal strength at the ultrasonictransmitter drive frequency may indicate the presence of bubble withinthe fluid delivery conduit 120. In various exemplary testingembodiments, a signal contrast ratio of, for example, approximatelybetween 2 and 5 may be indicative of the presence of a bubble within thefluid delivery conduit 120.

As described herein, the fluid sensor 10 is configured so as to enablethe simultaneous monitoring of both the AC and DC components of thepressure sensor output signal. Critically, such a configuration mayeffectively reduce the error rate of the sensor by compensating forunwarranted external forces that may affect the sensor’s acousticbaseline and lead in inaccuracies. Such a shift of the sensor’s acousticbaseline may be caused by factors such as, for example, tubing/plasticdeformation, temperature change, and/or fluid pressure that result in anunwarranted change of contact force to the sensor. Configuring thecomponents of the fluid sensor in such a way that enables the couplingof the AC and DC components enables the efficient and accuratecharacterization of flow within a fluid delivery conduit.

Conclusion

Many modifications and other embodiments will come to mind to oneskilled in the art to which this disclosure pertains having the benefitof the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that thedisclosure is not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A fluid sensor, the fluid sensor comprising:an ultrasonic transmitter configured to emit ultrasonic signals ; apressure sensor configured to detect pressure changes and to receive theultrasonic signals from the ultrasonic transmitter; and generate apressure output sensor signal based on the detected pressure changes andthe received ultrasonic signals; and a controller; wherein thecontroller is configured to detect a presence of at least one bubbleflowing through a fluid delivery conduit based at least in part on afrequency based analysis of the pressure sensor output signal.
 2. Thefluid sensor of claim 1, wherein the transmitter configured to emit theultrasonic signals through an emitting face and the pressure sensorreceives the ultrasonic signals through a receiving face.
 3. The fluidsensor of claim 2, wherein the emitting face of the ultrasonictransmitter is spaced apart from the receiving face of the pressuresensor to collectively define an adjustable gap configured to receivethe fluid delivery conduit.
 4. The fluid sensor of claim 1, furthercomprising a housing, wherein the housing comprises an exterior housingportion and an interior housing portion, and wherein the ultrasonictransmitter and the pressure sensor are enclosed within the interiorhousing portion.
 5. The fluid sensor of claim 4, wherein the interiorhousing portion further defines a channel configured to secure at leasta portion of the fluid delivery conduit within the interior housingportion and wherein at least a portion of the channel is aligned withthe gap.
 6. The fluid sensor of claim 1, wherein at least a portion ofthe fluid delivery conduit positioned within the gap is compressed suchthat at least substantially all of the receiving face of the pressuresensor is engaged by the portion of the fluid delivery conduit.
 7. Thefluid sensor of claim 1, wherein the pressure sensor comprises: apressure sensing element mounted to a substrate; and a forcetransmitting member positioned adjacent to the pressure sensing element,wherein the force transmitting member transmits a force applied to afront side of the force transmitting member to a front side of thepressure sensing element.
 8. The fluid sensor of claim 7, wherein theforce transmitting member is a gel.
 9. The fluid sensor of claim 1,wherein the controller is configured for wireless communication of anoutput signal.
 10. The fluid sensor of claim 1, wherein the ultrasonictransmitter is configured to receive a drive signal from the controller,wherein the drive signal comprises at least one of an AC component or aDC component.
 11. The fluid sensor of claim 1, wherein the ultrasonictransmitter comprises a piezoelectric ultrasonic transducer.
 12. Thefluid sensor of claim 1, wherein the fluid sensor is configured todetect a change in pressure within the fluid delivery conduit based atleast in part on a detected shift in a received signal.
 13. The fluidsensor of claim 1, wherein the controller is configured to constructtransformed data by performing a Fast Fourier Transform of the pressuresensor output signal, and wherein the transformed data is indicative ofa strength of the pressure sensor output signal across a frequencyrange.
 14. The fluid sensor of claim 13, wherein the fluid sensor isconfigured to detect the presence of the at least one bubble flowingthrough the fluid delivery conduit by measuring a detected change in thetransformed data at a frequency that is at least substantially similarto a drive frequency of the ultrasonic transmitter.
 15. A method ofdetecting at least one air bubble within a fluid delivery conduit of afluid sensor, the method comprising: receiving a received signal from anultrasonic transmitter at a pressure sensor, the pressure sensor beingconfigured to detect pressure changes and generate a pressure sensoroutput signal based at least in part on the received signal and thedetected pressure changes; and detecting the at least one air bubblewithin the fluid delivery conduit based at least in part on a frequencybased analysis of the pressure sensor output signal.
 16. The method ofclaim 15, further comprising emitting the received signal as ultrasonicsignals from the ultrasonic transmitter, through the fluid deliveryconduit, and to the pressure sensor aligned with the ultrasonictransmitter on an opposite side of the fluid delivery conduit andconfigured to receive the ultrasonic signals emitted from the ultrasonictransmitter.
 17. The method of claim 15, wherein a DC shift in thepressure sensor output signal corresponds to the change in pressurewithin the fluid delivery conduit.
 18. The method of claim 15, wherein acontroller is configured to construct transformed data by performing aFast Fourier Transform of the pressure sensor output signal, and whereinthe transformed data is indicative of a strength of the pressure sensoroutput signal across a frequency range.
 19. The method of claim 16,wherein detecting the at least one air bubble within the fluid deliveryconduit comprises: measuring the detected change in transformed data ata frequency that is at least substantially similar to a drive frequencyof the ultrasonic transmitter.
 20. The method of claim 19, wherein thefluid sensor comprises a bandpass filter centered at the drive frequencyof the ultrasonic transmitter to selectively distinguish the pressuresensor output signal at the drive frequency of the ultrasonictransmitter from noise present within the pressure sensor output signal.